THREE.TrackballControls = function ( object, domElement ) {

  var _this = this;
  var STATE = { NONE: - 1, ROTATE: 0, ZOOM: 1, PAN: 2, TOUCH_ROTATE: 3, TOUCH_ZOOM_PAN: 4 };

  this.object = object;
  this.domElement = ( domElement !== undefined ) ? domElement : document;

  // API

  this.enabled = true;

  this.screen = { left: 0, top: 0, width: 0, height: 0 };

  this.rotateSpeed = 1.0;
  this.zoomSpeed = 1.2;
  this.panSpeed = 0.3;

  this.noRotate = false;
  this.noZoom = false;
  this.noPan = false;

  this.staticMoving = false;
  this.dynamicDampingFactor = 0.2;

  this.minDistance = 0;
  this.maxDistance = Infinity;

  this.keys = [ 65 /*A*/, 83 /*S*/, 68 /*D*/ ];

  // internals

  this.target = new THREE.Vector3();

  var EPS = 0.000001;

  var lastPosition = new THREE.Vector3();

  var _state = STATE.NONE,
      _prevState = STATE.NONE,

      _eye = new THREE.Vector3(),

      _movePrev = new THREE.Vector2(),
      _moveCurr = new THREE.Vector2(),

      _lastAxis = new THREE.Vector3(),
      _lastAngle = 0,

      _zoomStart = new THREE.Vector2(),
      _zoomEnd = new THREE.Vector2(),

      _touchZoomDistanceStart = 0,
      _touchZoomDistanceEnd = 0,

      _panStart = new THREE.Vector2(),
      _panEnd = new THREE.Vector2();

  // for reset

  this.target0 = this.target.clone();
  this.position0 = this.object.position.clone();
  this.up0 = this.object.up.clone();

  // events

  var changeEvent = { type: 'change' };
  var startEvent = { type: 'start' };
  var endEvent = { type: 'end' };


  // methods

  this.handleResize = function () {

      if ( this.domElement === document ) {

          this.screen.left = 0;
          this.screen.top = 0;
          this.screen.width = window.innerWidth;
          this.screen.height = window.innerHeight;

      } else {

          var box = this.domElement.getBoundingClientRect();
          // adjustments come from similar code in the jquery offset() function
          var d = this.domElement.ownerDocument.documentElement;
          this.screen.left = box.left + window.pageXOffset - d.clientLeft;
          this.screen.top = box.top + window.pageYOffset - d.clientTop;
          this.screen.width = box.width;
          this.screen.height = box.height;

      }

  };

  this.handleEvent = function ( event ) {

      if ( typeof this[ event.type ] == 'function' ) {

          this[ event.type ]( event );

      }

  };

  var getMouseOnScreen = ( function () {

      var vector = new THREE.Vector2();

      return function getMouseOnScreen( pageX, pageY ) {

          vector.set(
              ( pageX - _this.screen.left ) / _this.screen.width,
              ( pageY - _this.screen.top ) / _this.screen.height
          );

          return vector;

      };

  }() );

  var getMouseOnCircle = ( function () {

      var vector = new THREE.Vector2();

      return function getMouseOnCircle( pageX, pageY ) {

          vector.set(
              ( ( pageX - _this.screen.width * 0.5 - _this.screen.left ) / ( _this.screen.width * 0.5 ) ),
              ( ( _this.screen.height + 2 * ( _this.screen.top - pageY ) ) / _this.screen.width ) // screen.width intentional
          );

          return vector;

      };

  }() );

  this.rotateCamera = ( function() {

      var axis = new THREE.Vector3(),
          quaternion = new THREE.Quaternion(),
          eyeDirection = new THREE.Vector3(),
          objectUpDirection = new THREE.Vector3(),
          objectSidewaysDirection = new THREE.Vector3(),
          moveDirection = new THREE.Vector3(),
          angle;

      return function rotateCamera() {

          moveDirection.set( _moveCurr.x - _movePrev.x, _moveCurr.y - _movePrev.y, 0 );
          angle = moveDirection.length();

          if ( angle ) {

              _eye.copy( _this.object.position ).sub( _this.target );

              eyeDirection.copy( _eye ).normalize();
              objectUpDirection.copy( _this.object.up ).normalize();
              objectSidewaysDirection.crossVectors( objectUpDirection, eyeDirection ).normalize();

              objectUpDirection.setLength( _moveCurr.y - _movePrev.y );
              objectSidewaysDirection.setLength( _moveCurr.x - _movePrev.x );

              moveDirection.copy( objectUpDirection.add( objectSidewaysDirection ) );

              axis.crossVectors( moveDirection, _eye ).normalize();

              angle *= _this.rotateSpeed;
              quaternion.setFromAxisAngle( axis, angle );

              _eye.applyQuaternion( quaternion );
              _this.object.up.applyQuaternion( quaternion );

              _lastAxis.copy( axis );
              _lastAngle = angle;

          } else if ( ! _this.staticMoving && _lastAngle ) {

              _lastAngle *= Math.sqrt( 1.0 - _this.dynamicDampingFactor );
              _eye.copy( _this.object.position ).sub( _this.target );
              quaternion.setFromAxisAngle( _lastAxis, _lastAngle );
              _eye.applyQuaternion( quaternion );
              _this.object.up.applyQuaternion( quaternion );

          }

          _movePrev.copy( _moveCurr );

      };

  }() );


  this.zoomCamera = function () {

      var factor;

      if ( _state === STATE.TOUCH_ZOOM_PAN ) {

          factor = _touchZoomDistanceStart / _touchZoomDistanceEnd;
          _touchZoomDistanceStart = _touchZoomDistanceEnd;
          _eye.multiplyScalar( factor );

      } else {

          factor = 1.0 + ( _zoomEnd.y - _zoomStart.y ) * _this.zoomSpeed;

          if ( factor !== 1.0 && factor > 0.0 ) {

              _eye.multiplyScalar( factor );

          }

          if ( _this.staticMoving ) {

              _zoomStart.copy( _zoomEnd );

          } else {

              _zoomStart.y += ( _zoomEnd.y - _zoomStart.y ) * this.dynamicDampingFactor;

          }

      }

  };

  this.panCamera = ( function() {

      var mouseChange = new THREE.Vector2(),
          objectUp = new THREE.Vector3(),
          pan = new THREE.Vector3();

      return function panCamera() {

          mouseChange.copy( _panEnd ).sub( _panStart );

          if ( mouseChange.lengthSq() ) {

              mouseChange.multiplyScalar( _eye.length() * _this.panSpeed );

              pan.copy( _eye ).cross( _this.object.up ).setLength( mouseChange.x );
              pan.add( objectUp.copy( _this.object.up ).setLength( mouseChange.y ) );

              _this.object.position.add( pan );
              _this.target.add( pan );

              if ( _this.staticMoving ) {

                  _panStart.copy( _panEnd );

              } else {

                  _panStart.add( mouseChange.subVectors( _panEnd, _panStart ).multiplyScalar( _this.dynamicDampingFactor ) );

              }

          }

      };

  }() );

  this.checkDistances = function () {

      if ( ! _this.noZoom || ! _this.noPan ) {

          if ( _eye.lengthSq() > _this.maxDistance * _this.maxDistance ) {

              _this.object.position.addVectors( _this.target, _eye.setLength( _this.maxDistance ) );
              _zoomStart.copy( _zoomEnd );

          }

          if ( _eye.lengthSq() < _this.minDistance * _this.minDistance ) {

              _this.object.position.addVectors( _this.target, _eye.setLength( _this.minDistance ) );
              _zoomStart.copy( _zoomEnd );

          }

      }

  };

  this.update = function () {

      _eye.subVectors( _this.object.position, _this.target );

      if ( ! _this.noRotate ) {

          _this.rotateCamera();

      }

      if ( ! _this.noZoom ) {

          _this.zoomCamera();

      }

      if ( ! _this.noPan ) {

          _this.panCamera();

      }

      _this.object.position.addVectors( _this.target, _eye );

      _this.checkDistances();

      _this.object.lookAt( _this.target );

      if ( lastPosition.distanceToSquared( _this.object.position ) > EPS ) {

          _this.dispatchEvent( changeEvent );

          lastPosition.copy( _this.object.position );

      }

  };

  this.reset = function () {

      _state = STATE.NONE;
      _prevState = STATE.NONE;

      _this.target.copy( _this.target0 );
      _this.object.position.copy( _this.position0 );
      _this.object.up.copy( _this.up0 );

      _eye.subVectors( _this.object.position, _this.target );

      _this.object.lookAt( _this.target );

      _this.dispatchEvent( changeEvent );

      lastPosition.copy( _this.object.position );

  };

  // listeners

  function keydown( event ) {

      if ( _this.enabled === false ) return;

      window.removeEventListener( 'keydown', keydown );

      _prevState = _state;

      if ( _state !== STATE.NONE ) {

          return;

      } else if ( event.keyCode === _this.keys[ STATE.ROTATE ] && ! _this.noRotate ) {

          _state = STATE.ROTATE;

      } else if ( event.keyCode === _this.keys[ STATE.ZOOM ] && ! _this.noZoom ) {

          _state = STATE.ZOOM;

      } else if ( event.keyCode === _this.keys[ STATE.PAN ] && ! _this.noPan ) {

          _state = STATE.PAN;

      }

  }

  function keyup( event ) {

      if ( _this.enabled === false ) return;

      _state = _prevState;

      window.addEventListener( 'keydown', keydown, false );

  }

  function mousedown( event ) {

      if ( _this.enabled === false ) return;

      event.preventDefault();
      event.stopPropagation();

      if ( _state === STATE.NONE ) {

          _state = event.button;

      }

      if ( _state === STATE.ROTATE && ! _this.noRotate ) {

          _moveCurr.copy( getMouseOnCircle( event.pageX, event.pageY ) );
          _movePrev.copy( _moveCurr );

      } else if ( _state === STATE.ZOOM && ! _this.noZoom ) {

          _zoomStart.copy( getMouseOnScreen( event.pageX, event.pageY ) );
          _zoomEnd.copy( _zoomStart );

      } else if ( _state === STATE.PAN && ! _this.noPan ) {

          _panStart.copy( getMouseOnScreen( event.pageX, event.pageY ) );
          _panEnd.copy( _panStart );

      }

      document.addEventListener( 'mousemove', mousemove, false );
      document.addEventListener( 'mouseup', mouseup, false );

      _this.dispatchEvent( startEvent );

  }

  function mousemove( event ) {

      if ( _this.enabled === false ) return;

      event.preventDefault();
      event.stopPropagation();

      if ( _state === STATE.ROTATE && ! _this.noRotate ) {

          _movePrev.copy( _moveCurr );
          _moveCurr.copy( getMouseOnCircle( event.pageX, event.pageY ) );

      } else if ( _state === STATE.ZOOM && ! _this.noZoom ) {

          _zoomEnd.copy( getMouseOnScreen( event.pageX, event.pageY ) );

      } else if ( _state === STATE.PAN && ! _this.noPan ) {

          _panEnd.copy( getMouseOnScreen( event.pageX, event.pageY ) );

      }

  }

  function mouseup( event ) {

      if ( _this.enabled === false ) return;

      event.preventDefault();
      event.stopPropagation();

      _state = STATE.NONE;

      document.removeEventListener( 'mousemove', mousemove );
      document.removeEventListener( 'mouseup', mouseup );
      _this.dispatchEvent( endEvent );

  }

  function mousewheel( event ) {

      if ( _this.enabled === false ) return;

      event.preventDefault();
      event.stopPropagation();

      switch ( event.deltaMode ) {

          case 2:
              // Zoom in pages
              _zoomStart.y -= event.deltaY * 0.025;
              break;

          case 1:
              // Zoom in lines
              _zoomStart.y -= event.deltaY * 0.01;
              break;

          default:
              // undefined, 0, assume pixels
              _zoomStart.y -= event.deltaY * 0.00025;
              break;

      }

      _this.dispatchEvent( startEvent );
      _this.dispatchEvent( endEvent );

  }

  function touchstart( event ) {

      if ( _this.enabled === false ) return;

      switch ( event.touches.length ) {

          case 1:
              _state = STATE.TOUCH_ROTATE;
              _moveCurr.copy( getMouseOnCircle( event.touches[ 0 ].pageX, event.touches[ 0 ].pageY ) );
              _movePrev.copy( _moveCurr );
              break;

          default: // 2 or more
              _state = STATE.TOUCH_ZOOM_PAN;
              var dx = event.touches[ 0 ].pageX - event.touches[ 1 ].pageX;
              var dy = event.touches[ 0 ].pageY - event.touches[ 1 ].pageY;
              _touchZoomDistanceEnd = _touchZoomDistanceStart = Math.sqrt( dx * dx + dy * dy );

              var x = ( event.touches[ 0 ].pageX + event.touches[ 1 ].pageX ) / 2;
              var y = ( event.touches[ 0 ].pageY + event.touches[ 1 ].pageY ) / 2;
              _panStart.copy( getMouseOnScreen( x, y ) );
              _panEnd.copy( _panStart );
              break;

      }

      _this.dispatchEvent( startEvent );

  }

  function touchmove( event ) {

      if ( _this.enabled === false ) return;

      event.preventDefault();
      event.stopPropagation();

      switch ( event.touches.length ) {

          case 1:
              _movePrev.copy( _moveCurr );
              _moveCurr.copy( getMouseOnCircle( event.touches[ 0 ].pageX, event.touches[ 0 ].pageY ) );
              break;

          default: // 2 or more
              var dx = event.touches[ 0 ].pageX - event.touches[ 1 ].pageX;
              var dy = event.touches[ 0 ].pageY - event.touches[ 1 ].pageY;
              _touchZoomDistanceEnd = Math.sqrt( dx * dx + dy * dy );

              var x = ( event.touches[ 0 ].pageX + event.touches[ 1 ].pageX ) / 2;
              var y = ( event.touches[ 0 ].pageY + event.touches[ 1 ].pageY ) / 2;
              _panEnd.copy( getMouseOnScreen( x, y ) );
              break;

      }

  }

  function touchend( event ) {

      if ( _this.enabled === false ) return;

      switch ( event.touches.length ) {

          case 0:
              _state = STATE.NONE;
              break;

          case 1:
              _state = STATE.TOUCH_ROTATE;
              _moveCurr.copy( getMouseOnCircle( event.touches[ 0 ].pageX, event.touches[ 0 ].pageY ) );
              _movePrev.copy( _moveCurr );
              break;

      }

      _this.dispatchEvent( endEvent );

  }

  function contextmenu( event ) {

      event.preventDefault();

  }

  this.dispose = function() {

      this.domElement.removeEventListener( 'contextmenu', contextmenu, false );
      this.domElement.removeEventListener( 'mousedown', mousedown, false );
      this.domElement.removeEventListener( 'wheel', mousewheel, false );

      this.domElement.removeEventListener( 'touchstart', touchstart, false );
      this.domElement.removeEventListener( 'touchend', touchend, false );
      this.domElement.removeEventListener( 'touchmove', touchmove, false );

      document.removeEventListener( 'mousemove', mousemove, false );
      document.removeEventListener( 'mouseup', mouseup, false );

      window.removeEventListener( 'keydown', keydown, false );
      window.removeEventListener( 'keyup', keyup, false );

  };

  this.domElement.addEventListener( 'contextmenu', contextmenu, false );
  this.domElement.addEventListener( 'mousedown', mousedown, false );
  this.domElement.addEventListener( 'wheel', mousewheel, false );

  this.domElement.addEventListener( 'touchstart', touchstart, false );
  this.domElement.addEventListener( 'touchend', touchend, false );
  this.domElement.addEventListener( 'touchmove', touchmove, false );

  window.addEventListener( 'keydown', keydown, false );
  window.addEventListener( 'keyup', keyup, false );

  this.handleResize();

  // force an update at start
  this.update();

};

THREE.TrackballControls.prototype = Object.create( THREE.EventDispatcher.prototype );
THREE.TrackballControls.prototype.constructor = THREE.TrackballControls;
